Brazing process

Abstract

Ferrous parts are bonded together in a copper brazing furnace under suitable temperatures and a furnace atmosphere which, in the absence of parts, is comprised of at least 90% nitrogen, up to 7% combined hydrogen and carbon monoxide with hydrogen being greater than 50% of the total of CO and H 2 and having a dew point between approximately -40° to +10° C. In the preheat section of a continuous belt furnace or the like, the dew point may range between -20° to +10° C. while in the furnace hot zone, the dew point is maintained between approximately -40° to -10° C. A brazing paste which is preferably a combined copper and 25-75% copper oxide paste is utilized. With such furnace atmosphere and paste composition, clean part surfaces, which permit superior wetting by molten copper and thus acceptable copper flow and penetration into the joint being bonded, are obtainable. The furnace atmospheres utilized enable increased life to be obtained from furnace materials such as brick insulation, muffles, conveyor belts, and heating elements.

I claim: 
     
       1. A process for copper brazing ferrous parts in a continuous furnace comprising the steps of: heating said furnace to establish a region therein at a temperature of at least 600° C.; establishing an atmosphere in said region under equilibrium conditions in the absence of parts comprised of at least 90% nitrogen, at total of about 1.0 to 7.0% hydrogen and carbon monoxide, wherein the concentration of hydrogen is greater than the concentration of carbon monoxide, and moisture sufficient to provide a dew point of about -40° C. to +10° C.; and passing through said furnace said ferrous parts having thereon a brazing paste comprised of a copper paste and 25-75% of a copper oxide paste whereby said parts are brazed. 
     
     
       2. The process defined in claim 1 wherein said atmosphere includes 0-2.0% carbon dioxide. 
     
     
       3. The process defined in claim 2 wherein the combined construction of moisture and carbon dioxide of said atmosphere does not exceed about 3.0%. 
     
     
       4. The process defined in claim 1 wherein the atmosphere in the portion of said furnace under an increasing temperature in the direction of travel of said parts between 600°-900° C. exhibits a dew point between -20° to +10° C. 
     
     
       5. The process defined in claim 1 wherein a portion of said furnace is heated to a brazing temperature of at least 850° C. and the atmosphere in the portion of said furnace having a decreasing temperature in the direction of travel of said parts between said brazing temperature and 600° C. exhibits a dew point in the range of -40° to -10° C. 
     
     
       6. A process for copper brazing ferrous parts in a continuous furnace having at least one region heated to a temperature of at least 600° C. comprising: (a) providing an atmosphere in said furnace under equilibrium conditions in the absence of parts comprised of at least 90% nitrogen, from about 1.0% to 7.0% hydrogen and carbon monoxide, wherein the concentration of hydrogen is greater than the concentration of carbon monoxide, and moisture sufficient to provide a dew point of between about -40° C. and +10° C.;   (b) applying to said ferrous parts a brazing mixture comprising 25-75% copper oxide paste and the balance a copper paste; and   (c) passing said parts through a region of said furnace at a temperature sufficient to cause brazing of said parts.   
     
     
       7. The process of claim 6 wherein said atmosphere further comprises from 0% to 2.0% carbon dioxide. 
     
     
       8. The process of claim 7 wherein the combined concentration of moisture and carbon dioxide in said atmosphere does not exceed about 3.0%. 
     
     
       9. The process of claim 6 wherein said atmosphere is comprised of about 1% combined hydrogen and carbon monoxide. 
     
     
       10. The process of claim 6 wherein said furnace contains a first region heated to a temperature of between about 600° to 900° C. and said atmosphere in said first region contains sufficient moisture to provide a dew point of between about -20° C. and +10° C. 
     
     
       11. The process of claim 6 wherein said furnace contains a second region heated to a temperature of from about 850° C. to 1150° C. and said atmosphere in said second region contains sufficient moisture to provide a dew point of between about -40° C. and +10° C. 
     
     
       12. A process for the copper brazing of ferrous parts in a continuous furnace having a preheat zone varying in temperature from about 600° C. to about 900° C. and a hot zone varying in temperature from about 850° C. to about 1150° C. comprising: (a) providing a first atmosphere in said preheat zone under equilibrium conditions in the absence of parts comprised of at least 90% nitrogen, from about 1.0% to 7.0% hydrogen and carbon monoxide wherein the concentration of hydrogen is greater than the concentration of carbon monoxide and moisture sufficient to provide a dew point of from about -20° C. to +10° C.;   (b) providing a second atmosphere in said hot zone under equilibrium conditions in the absence of parts comprised of at least 90% nitrogen, from about 1.0% to 7.0% hydrogen and carbon monoxide wherein the concentration of hydrogen is greater than the concentration of carbon monoxide and moisture sufficient to provide a dew point of from about -40° C. to -10° C., the dew point of said first atmosphere being greater than the dew point of said second atmosphere;   (c) applying to said ferrous parts a copper containing brazing paste; and   (d) passing said parts through said preheat zone and said hot zone to cause brazing thereof.   
     
     
       13. The process of claim 12 wherein said atmosphere further comprises from 0% to 2.0% carbon dioxide. 
     
     
       14. The process of claim 12 wherein said atmosphere is comprised of about 1% combined hydrogen and carbon monoxide. 
     
     
       15. A process as defined in claim 12 wherein said furnace includes a zone after the hot zone in the direction of travel of said parts wherein the temperature is below 600° C. and additionally comprising the step of maintaining an atmosphere consisting essentially of nitrogen in said zone.